1. Field of the Invention
This invention is related to diamond type drag bits that utilize hydraulic energy to enhance earth formation penetration rates.
More particularly, this invention relates to diamond type drag bits having a superior means to utilize hydraulic energy passing through the bit to cool and clean as well as scavenge a borehole bottom during rock bit operation.
2. Description of the Prior Art
There are a number of diamond type drag bit patents that address the problem of cooling and cleaning diamond cutting elements during rock bit operation.
For example, U.S. Pat. No. 4,253,533, assigned to the same assignee as the present invention, describes a diamond studded insert drag bit having a multiplicity of individual diamond insert cutter blanks inserted in the face of the bit. The diamond insert blanks are so positioned to maximize penetration of the bit in a borehole. The bit further includes a pair of wear pads adjacent the several diamond insert cutter blanks, the wear pads serving to limit the insert penetration depth while channeling the flow of drilling mud emanating from fluid passages formed in the face of the bit. The wear pads seal off a portion of the borehole bottom, thereby directing hydraulic fluid across the face and over each of the strategically positioned diamond cutter blanks.
While this patent has proven satisfactory in operation, it has not provided an even distribution of crossflow fluid to each of the diamond cutter blanks. For example, energy velocity is dissipated as flow reaches the outer peripheral edge of the bit, thus some of the insert blanks near the gage of the bit tend to be more effected by heat buildup and the like.
Another patent, U.S. Pat. No. 4,246,977, also assigned to the same assignee as the present invention, describes a diamond studded insert drag bit having a multiplicity of individual diamond insert cutter blanks inserted in the face of the bit. The diamond blanks are so positioned to maximize penetration of the bit in a borehole. The bit further includes fluid passages strategically located in the bit face to provide uniform flow, cooling, and continuous cleaning of each of the diamond cutter insert blanks. The fluid passages are so sized to cause minimum bit pressure drop. While this invention did evenly distribute fluid over the diamond cutters, the design did not adequately scavenge the borehole bottom to efficiently remove detritus therefrom.
Another prior art patent, U.S. Pat. No. 4,492,277, describes a drag bit for drilling a rock formation having a bit face matrix for supporting a plurality of cutters, the matrix having one or more fluid passages for discharging a fluid to flow over the bit face. To enhance the cooling and cleaning of the plurality of cutters, the bit face matrix includes a "crow's foot" type port that directs fluid into a restricted area formed between the bit face and the formation. A high velocity radial fluid flow across the bit face matrix is the desired effect. The fluid flow prevents debris from accumulating on the plurality of cutters thus providing cooling thereof. The patent teaches improved fluid distribution. A spiraling type dam structure is illustrated that extends from the nozzle radially outward over most of the bit face matrix.
This patent does not provide a uniform flow of fluid from the crow's foot fluid opening to each of the cutters randomly positioned on the face of the bit.
The present invention overcomes the shortcomings of the foregoing prior art patents by providing large plenum chambers in the cutting face of the bit which are adapted to receive fluid from the interior of the drag bit, thus providing better than fifty percent borehole bottom coverage with high pressure drilling fluid. A series of diamond cutters are mounted on the raised lands that defines and forms each plenum chamber. The highly turbulent fluid confined within the plenum chambers is then uniformly accelerated past each of the diamond cutters mounted on the raised lands. The abundance of turbulent hydraulic energy made available by the large plenum chambers serves to more aggressively scavenge the borehole bottom of detritus while simultaneously cleaning and cooling each of the diamond cutters mounted in the raised lands. Moreover, the plenum chambers, being surrounded by closely spaced cutter elements, enable a multiplicity of diamond cutters to be positioned adjacent the gage of the borehole, thus providing good rock formation penetrating qualities while providing superior gage cutting capabilities.